1. Field of the Invention
The present invention relates to light-weight plywood constructions, more particularly the present invention relates to Paulowina based plywood constructions.
2. Background Information
Plywood is a wood product manufactured out of many sheets of veneer, or plies, pressed together and glued, with their grains typically going in opposite directions. Plywood tends to be extremely strong, though often not very attractive. Plywood is treated in many different ways depending upon its intended application. Plywood, due to the manner which it is constructed, also tends to resist cracking, bending, warping, and shrinkage, depending upon its thickness. Plywood is also referred to as an engineered wood, although it is made from a composite of wooden materials, and various forms of it have been made for thousands of years. Plywood structures have also been referenced as laminated veneer lumber or LVL in some of the literature.
The plies that form plywood are generally cut on a rotary lathe, which cuts a continuous roll of wood while a log, called a peeler, is turned against it. Rotary lathing is rapid and makes efficient use of the wood while turning out veneers highly suitable for plywood. Some lathes are designed to expose more interesting parts of the wood grain, although they may be more wasteful of the wood. Rotary lathed veneers tend to be dull in appearance, although perfectly functional. After the veneers are cut, they are overlaid with layers of glue and pressed together until dry to form a flat, even, tight piece of plywood. Plywood is sturdier than regular sheets or panels of wood, because the veneers are laid with their grains opposing, which also causes the wood product to resist warping because the grains pull each other tight.
Plywood comes in a number of forms, including softwood plywood, which is made from pine, fir, or spruce. For example, commercial plywood has been made from rotary-peeled Douglas-fir veneers and from Southern yellow pine veneers. Softwood plywood is usually pale in color and is used in construction applications.
As a point of reference, many people are familiar with the concepts of hardwood and softwood. However, few people know why woods are split into these two categories, and make the assumption that hardwoods are hard, while softwood is soft. This distinction is incorrect: balsa wood, for example, is classified as a hardwood despite the fact that it is very soft and light.
Softwood and hardwood are actually distinguished botanically, not by their end use or appearance. In general, hardwood comes from a deciduous tree which loses its leaves annually, and softwood comes from a conifer, which usually remains evergreen. Hardwoods tend to be slower growing, and are therefore usually more dense, but not always.
Hardwoods is a very extensive listing and a non-exclusive list includes Alder, Applewood, Ash, Aspen, Balsa, Basswood, Beech, Birch, Blackbean, Blackwood, Bocote, Boxwood, Brazilwood, Bubing a, Buckeye, Butternut, Carapa, Catalpa, Cherry, Chestnut, Coachwood, Cocobolo, Corkwood, Cottonwood, Dogwood, Ebony, Elm, Eucalyptus, Greenheart, Grenadilla, Gum, Hickory, Hornbeam, Hophornbeam, Ipe, Iroke, Ironwood, Brazilian Rosewood, Jatoba, lacewood, Laurel, Limba, Lignum Vitae, Locust, Mahogany, Maple, Meranti, Merawan, Mpingo, Oak, Obeche, Okoume, Paulownia Pear, Poplar, Ramin, Redcedar, Rosewood, Sal, Sapale Sandalwood, Sassafras, Satinwood, Silver Wattle, Snakewood, Sourwood, Spanish Cedar, Sycamore, Teak, Walnut, Willow and Yellow Poplar. More exotic hardwoods also exist. Many of these are available as commercial hardwoods.
Softwood usually grows in huge tracts of trees which may spread for miles, while hardwoods tend to be found mixed with a variety of other species. Some examples of softwood include pine, redwood, fir, cedar, and larch.
Returning to the topic of plywood, mahogany or birch are used to create an extremely strong type of plywood known as aircraft plywood, because it was utilized in the construction of aircraft through the Second World War.
If plywood is destined for indoor use, it is conventionally made with urea-formaldehyde glue, which dries quickly and is inexpensive. For plywood intended for use in outdoor applications or wet environments, a more expensive water resistant glue is used to prevent the plies from coming apart, or delaminating, and compromising the strength of the plywood.
Plies typically range in thickness depending upon the plywood panels they are used in, from 1/10 inch (approximately ⅕ centimeter) to ⅙ inch (almost ⅕ centimeters). Standard plywood sizes consist of four foot by eight foot (1.2 by 2.4 meter) sheets in three, five, or seven plies. The end user can cut, reshape, or sand these sheets to needed specifications.
Most plywood is made using the same species of wood. However, U.S. Pat. No. 5,040,582 discloses a multi species laminated veneer lumber (a specialty plywood used for lumber manufacture), as well as laminated veneer lumber made from the combination of hardwoods and softwoods. This teaching notes the difference in shrinkage and expansion between the different wood species, particularly between high and low density wood species. This reference teaches that the species sequence from face to core must be identical or very similar on either side of the center ply when an odd number of plies are used or on either side of the center line when an even number of plies are used.
U.S. Pat. No. 5,234,747 teaches a symmetrical lay-up of, from top to bottom, multiple plies of a low density, 6% to 15% moisture content spruce, multiple plies of a high density, less than 5% moisture content Douglas fir, and multiple plies of a low density, 6% to 15% moisture content spruce.
U.S. Pat. No. 7,261,947 discloses a plywood laminate having dimensional stability and resistance to warping and de-lamination is formed from a plurality of higher quality plies and a plurality of lower quality plies. The higher quality plies may be of hardwood and the lower quality plies may be of softwood or lower quality hardwoods, or the higher quality plies may have a veneer grade of better than ANSI/HPVA HP-1-2000 veneer grade C and the lower quality plies may have a veneer grade of no greater than ANSI/HPVA HP-1-2000 veneer grade C.
U.S. Patent Publication 2007-0125446 teaches a method of producing a fireproof plywood from perennial grasses, such as Arundo donax Ligneous, various bamboo strains, or a blend thereof, by first weaving the stalks of these plants into a mat and then layering these mats and binding each layer with any one of several commercial resins mixed with potash for the purpose of enhancing the final product's fire retardant quality.
U.S. Patent Publication 2007-0125446 teaches a plywood composed of several layers of carbon fabrics and veneers which are symmetrically placed within the plywood, where a hot-melt adhesive is used to adhere the adjacent layers. Further, a suitably high temperature and high pressure are provided at the same time to melt the hot-melt adhesive and make the carbon fabrics and veneers adhere tightly. This plywood composed by carbon fabrics and veneers has a higher toughness and thinner thickness compared with conventional plywood.
The increase in energy, e.g., gasoline prices, has brought a demand from the producers and manufacturers of Recreational vehicles, campers, shipping container, boats, trucking companies, kitchens, cabinet makers and any other industry that needs to reduce the shipping budget by reducing their overall gasoline or fuel consumption. Further, the kitchen/bathroom cabinetry industry is also in need of a lightweight construction material to be used for such products as items as cabinets, bay/bow windows, speaker boxes, coffins, furniture, and bookshelves. These industries have relied heavily on plywood constructions. There remains a need in the art to for a light-weight plywood for such applications.